Blender animation to UNITY
I believe it's best to just make this animation in Unity itself. How did you import this animation to unity? Legacy? Was the rock animated seperately? if it was, you could add a script to it, that plays the animation and then destroys the rock gameobject, or you could make an animation in unity and make the gameObject invisible.
one way of coding that in C#: 

    Transform.Find("Rock").gameObject.enabled = false;


or, if you've made a prefab of the rock, you could just destroy it, and spawn it again if you need it:

    Destroy(Transform.Find("Rock"));